At the close of 2012, the UK had 83 million mobile subscribers, according to January estimates from the research firm. Of these, 36 million were smartphones and 47 million were non-smartphones. This represents a market penetration of 130%, according to Portio, which means there isn’t much room to add new mobile subscribers. Instead development in the market is happening around the shift toward smartphones and away from feature phones. Portio expects the number of smartphones in use to increase each year, with corresponding decreases in the number of non-smartphones.

These two trends may combine to push UK smartphone penetration above 50% this year, the study found. eMarketer’s slightly more conservative estimate has UK smartphone user penetration at 45.5% by year end, reaching 55% by 2014.

By 2016, Portio Research expects that roughly three-quarters of UK mobile devices will be smartphones, creating a mobile advertising environment in which smartphones are the rule, not the exception. Portio estimates that there will be 63 million smartphones and 21 million non-smartphones in the UK at that time.

According to eMarketer’s forecast, UK smartphone penetration will reach 78% of mobile phone users in 2016, continuing to stretch its lead as the country with the highest smartphone penetration in Western Europe. eMarketer projects that the UK’s smartphone penetration will overtake the US’s in 2016 as well—only South Korea, Japan and Australia will have higher percentages of mobile users on smartphones.